2 hours? Maybe. That assumes you get out of the plane (with everyone getting their bags from the overhead bins and standing up as soon as the plane stops, if not before) and out of the airport in 5 minutes (unlikely) and that you would get back to the airport an hour before your next fight. Of course, if you're doing this during rush hour, estimates could be off. Most important thing: know in advance what you want to see.

In all honesty, I am not the biggest fan of Neimeyer (to me Brasilia-- which we visited just a week ago-- looks like the Jetsons Meets East Berlin, or a city of the future Disney might have envisioned in the late 1950s), but to each their own). A bit too much of "hotel sector," "apartment sector" "fun sector," etc. Notably Neimeyer (still kicking at 105) lives in Rio.

I paid nearly R$40 to gt from the airport to my hotel, near the TV tower, as I recall, but your R$100 might still be enough for 2 hours. Allow at least 15-20 minutes to get from the airport to the main esplanade area. Map out in advance exacty what you want to see (i.e., don't just ask the taxi driver to show you the city). You may not have time to see much more than the outsides of buildings for the most part. You could, for example, head for the Congressional building complex, but the tours take ovr an hour so you may have time just to see the outside (the inside isn't architecturally interesting, anyway, from what we saw during the tour). The main museum is looks a bit like the flying saucer in "The Day the Earth Stood Still," though white. The outside if the best part (inside kind of spartan). so just driving by may be enough. National cathedral easy to see as a quick stop. If that's enough for you, you may have time. On Wednesdays, the presidential residence (well, where the prez lives part of the time) is open for tours but I don't think you'd have time. I'd forget taking the time to see the bridge over the lagoa. If you speak no Portuguese, giving directions and getting info could be tough.

Brasilia's airport is not bad, at least until you get to the very crowded, donut-shaped gate area.